A mixture of blood with antigen A and blood containing antibody a will?

Analyze the question The question asks what happens when blood containing antigen A is mixed with blood containing antibody a (anti-A).

Concept

• Antigens are found on the surface of red blood cells (e.g., antigen A in blood group A).
• Antibodies are found in the plasma (e.g., antibody a, or anti-A, in blood group B).
• An antibody binds specifically to its matching antigen. When antigen A meets antibody a, the red blood cells clump together. This clumping is called agglutination.

Step-by-step solution

1. Blood with antigen A is group A or group AB.
2. Blood with antibody a (anti-A) is group B or group O.
3. Mixing them brings antigen A into contact with its matching antibody.
4. The antibody binds the antigen and the red cells stick together, which is agglutination.

Checking the options

• A. Lead to agglutination: Correct. This is the antigen-antibody reaction.
• B. Facilitate dissolution of clot: Wrong. Dissolving a clot is fibrinolysis, which has nothing to do with this reaction.
• C. No effect: Wrong. Matching antigen and antibody always react.
• D. Change the blood group: Wrong. The reaction does not alter anyone's blood group. It only causes clumping.

Answer: A. lead to agglutination

Exam tip: Remember "matching antigen and antibody means clumping." This is why blood transfusion needs compatible blood. For example, group A blood given to a group B person (who has anti-A) causes agglutination, which can be fatal. Group O is the universal donor because its red cells have no A or B antigens.